The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat a patient""s skin and subcutaneous tissue, particularly including skin resurfacing procedures.
In early dermatology procedures, cosmetic surgeons often employed chemical peels and/or dermabrasion techniques to remove outer layers of the patient""s skin to rejuvenate wrinkled skin or to remove skins disorders, such as acne, lesions, early skin cancer, etc. These dermabrasion and chemical procedures, however, are difficult to control, requiring great surgical skill. In addition, these somewhat inelegant techniques often cause excessive bleeding, collateral tissue damage and patient discomfort.
In an effort to overcome some of the limitations of dermabrasion and chemical peels, lasers have been developed for use in cosmetic surgery. Lasers have improved the accuracy of skin resurfacing procedures, and they have reduced collateral damage to the tissue surrounding and underlying the treatment site. In laser dermatology applications, a handpiece is typically used to guide the output of a laser to the patient""s skin, and to form a laser spot of a desired size on the region of the skin which is to be treated. The handpiece is typically attached to one end of an articulated arm which transmits the output of a medical laser (such as CO2 or Er: YAG lasers) to the handpiece and allows the handpiece a wide range of motion.
Although initially encouraging, lasers suffer from a number of drawbacks in dermatology procedures. In the first place, laser equipment can be very expensive because of the costs associated with the laser light sources. Moreover, those lasers which permit acceptable depths of necrosis (such as excimer lasers, erbium: YAG lasers, and the like) provide a very low volumetric ablation rate, requiring numerous passes over the same treatment area which amounts to longer procedural times. In addition, erbium: YAG lasers generally do not provide effective hemostasis during the procedure, resulting in excessive bleeding which disrupts the surgeon""s view of the treatment site. The CO2 lasers provide a higher rate of ablation and an increased depth of tissue necrosis than their erbium: YAG counterparts. On the other hand, CO2 lasers often create significant residual thermal injury to tissue at and surrounding the treatment site, which requires long healing periods for the patient. In addition, CO2 lasers are associated with much pain and, therefore, require a lot of anesthesia, which increases the cost and length of the procedure.
Monopolar electrosurgical instruments have been used to effect electrodessication of abnormalities, such as lesions, skin tags, viral warts, pigment nevi, moles and skin cancer. For example, Conmed Corporation manufacturers a monopolar device, termed the Hyfrecator(trademark) having a single active electrode at the tip of an electrosurgical probe. In these procedures, the skin abnormality is typically removed with a scalpel, and a low voltage is applied to the active electrode in contact with the target tissue to deliver electric current through the tissue and the patient to a dispersive pad or indifferent electrode. The voltage desiccates the remaining abnormal tissue, and coagulates severed blood vessels at the target site. The remaining tissue is then removed with a sponge or similar material. The voltage generally must be low enough to prevent charring and potential scarring of the underlying dermis.
These electrosurgical devices and procedures, however, suffer from a number of disadvantages. For example, conventional electrosurgical cutting devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a xe2x80x9ccutting effectxe2x80x9d along the pathway of localized tissue heating. This cutting effect generally results in the production of smoke, or an electrosurgical plume, which can spread bacterial or viral particles from the tissue to the surgical team or to other portions of the patient""s body. In addition, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site.
Another disadvantage with current techniques of skin resurfacing is that these techniques typically require the ablation or removal of all or at least a portion of the patient""s epidermis layer. Removing the epidermis provides some beneficial effects, such as allowing for the creation of a neo-epidermis, removing or reducing sun discolorations and improving the superficial skin texture. However, this removal of the epidermis layer necessitates the use of wound dressing until a new epidermis is created, which greatly increases the pain and lengthens the healing time of the procedure.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures on the external surface of a patient""s body. The systems and methods of the present invention are particularly useful in skin resurfacing, i.e., removing or reducing wrinkles in the patient""s dermis tissue. The techniques of the present invention generally involve the selected application of energy to the patient""s dermis tissue to generate the growth of new collagen in this tissue, while minimizing the energy applied to the outer epidermis layer, thereby minimizing or suppressing the wound healing phase of the procedure.
In one aspect of the invention, a method includes positioning a first electrode adjacent to, or in contact with, a region on or within a patient""s skin, and applying a sufficient high frequency voltage between the first electrode and a second electrode to create a heat injury to a target tissue within the patient""s dermis layer without ablating the epidermis layer overlying the target tissue. Typically, the voltage applied to the first and second electrodes is sufficient to induce heating of the dermis layer to about 60xc2x0-80xc2x0 C., preferably about 65xc2x0-75xc2x0 C. This induced heating causes the patient""s body to undergo a wound healing response in the slightly inflamed tissue of the dermis. The wound healing process involves the generation of neo-collagen in the dermis layer, which fills in the wrinkle in the patient""s skin. In the present invention, this stimulation of collagen growth within the dermis is accomplished while minimizing or suppressing the damage caused to the outer epidermis layer, which reduces the overall pain and wound healing time for the patient.
In one embodiment, the first and second electrodes are positioned on the outer surface of the patient""s skin, and high frequency voltage is applied therebetween. The electrodes are spaced, sized and otherwise configured such that an electric current passes from the first electrode, through the epidermis layer to the target tissue in the dermis layer, and to the second electrode. Specifically, electrodes are selected with large surface areas that present a substantially uniform current density to minimize high current densities at the electrode surfaces, thereby generating a maximum current density within the dermis. The electrodes are spaced a sufficient distance to allow the electric current to penetrate the epidermis and pass through the dermis. In a preferred embodiment, the electrodes are positioned on either side of a wrinkle in the patient""s skin, and translated along the length of the wrinkle as high frequency voltage is applied therebetween.
In the representative embodiment, the first and second electrodes comprise spherical or hemispherical electrodes coupled to electrode support members that separate the electrodes from each other by a selected distance, typically about 5 to 20 cm. The spherical electrodes have a smooth outer surface to minimize current densities on this surface and to provide a homogenous current distribution around the electrodes. The electrode support members typically comprise a conductive shaft surrounded by an insulating jacket, or an insulating shaft that houses the electrical connections. The electrode support members service to electrically and mechanically couple the electrodes to a probe or handpiece for manipulation by the physician. The handpiece or probe is, in turn, coupled to a high frequency power supply for applying high frequency voltage through the handpiece to the electrodes. In one embodiment, the distance between the electrodes may be varied by the physician through an input control on the handpiece.
In a specific configuration, electrically conductive fluid is provided between each of the first and second electrodes and the patient""s skin to improve the contract between the electrodes and the skin. In one embodiment, an electrically conductive gel is applied to the skin surface to create a low impedance current path through the gel. In another embodiment, a conductive hydrogel is coated on the electrode surfaces. The hydrogel may also be soaked within a conductive fluid, such as isotonic saline, to create a slippery conductive interface with the patient""s skin, while minimizing skin surface conduction. The hydrogel does not retain as much heat as a conventional gel on the skin, which reduces the thermal injury to the patient""s skin.
In another embodiment, the first electrode is advanced through the patient""s epidermis layer to the underlying dermis layer, and high frequency voltage is applied between the first and second electrodes to effect heating of the dermis layer. In this embodiment, the first electrode functions as an active electrode and the second electrode functions as the return electrode. The first electrode comprises a sharp tapered distal end for mechanically advancing a portion of the electrode through the skin to the dermis layer. The second or return electrode may be a dispersive return pad positioned on the surface of the patient""s skin. In another embodiment, the second electrode is also advanced through the patient""s epidermis layer to the underlying dermis such that the electric current is confined to the dermis layer. In these embodiments, both electrodes may have similar shapes, and thus, both function as active or bi-active electrodes. In some embodiments, additional active and/or return electrodes may be advanced into the patient""s skin to more precisely control the heat injury within the dermis.
In a specific configuration, an electrode array of needle-shaped electrodes are advanced through the epidermis into the underlying dermis. The outer periphery of needle electrodes have a separate polarity from one or more of the inner electrodes to cause current flow therebetween. This configuration confines the current flow to an area within the electrode array.
In the representative embodiment, an electrosurgical probe or handpiece comprises a shaft or handle coupled to an electrode support at the distal end of the shaft or handle. The electrode support mechanically and electrically couples an electrode assembly to the probe or handpiece. The electrode assembly comprises an array of needle shaped electrodes designed for advancing through the patient""s skin. In this embodiment, the needle shaped electrodes include a proximal insulated portion for minimizing electric contact with the epidermis, and a distal exposed portion for applying electric current to the underlying dermis. In some embodiments, the probe will include a stop or other mechanism for controlling the depth of penetration of the electrodes in the patient""s skin.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.